Field of the Invention
The present invention relates to an electrophotographic member, a process cartridge, and an electrophotographic apparatus.
Description of the Related Art
An electrophotographic apparatus, which is an image forming apparatus using an electrophotographic method, includes an electrophotographic member such as a charging roller, a developing roller, and a transfer roller, and the electrophotographic member includes an electroconductive layer having an electric resistance value of approximately 1×103 to 1×1010Ω. To adjust the conductivity of the electroconductive layer, an ionic conductive agent such as quaternary ammonium salt compounds may be used.
A merit of the electroconductive layer given conductivity by the ionic conductive agent is that the electric resistance value is more uniform in such an electroconductive layer than that of the electroconductive layer given conductivity by an electron conductive agent such as carbon black.
Meanwhile, the conductivity of the electroconductive layer given conductivity by the ionic conductive agent is very strongly influenced by the moisture content. For example, the electric resistance value increases under a low temperature and low humidity environment, and decreases under a high temperature and high humidity environment. For this reason, it is difficult to maintain a desired conductivity irrespective of the environment.
A higher speed and higher definition of the electrophotographic apparatus these days will cause more image defects if the conductive roller has a higher resistance. For example, a higher resistance of the charging roller may cause horizontal streaks as image defects. A higher resistance of the developing roller will cause unevenness of an image.
The ionic conductive agent may gradually bleed from the inside of the electroconductive layer to the surface of the electroconductive layer as time passes (hereinafter, this phenomenon is also expressed as “bleeding”). As a result, the bleeding may cause change over time in the electric resistance value of the electroconductive layer, change over time in the outer diameter of the electrophotographic member, and adhesion of dirt to the surface of the electrophotographic member. For example, the outer shape of the charging roller may change due to the bleeding of the ionic conductive agent from the charging roller at a press contact portion between the charging roller and a photosensitive member to produce horizontal streaks on an image. For the developing roller, a toner or an external additive may adhere to the surface of the developing roller due to the bleeding of the ionic conductive agent from the developing roller to produce vertical streaks on an image.
Japanese Patent Application Laid-Open No. H10-196639 discloses a semiconductive roller given conductivity by an ionic conductive agent that suppresses the bleeding of the conductive agent while the electric resistance value of the semiconductive roller is adjusted to fall within a proper region independently of an environment in use. Specifically, the semiconductive roller includes a polyurethane elastic layer formed of a polyurethane resin prepared by adding a quaternary ammonium salt containing an ethylene glycol chain having a terminal hydroxy group when a polyol is reacted with a polyisocyanate.